This invention relates to an antilock brake device equipped with a pressure control valve and usable in a two-line brake circuit of an automotive vehicle.
FIG. 21 is a conceptual diagram of an antilock brake system (ABS). An antilock brake device 104, comprised of several solenoid valves, a pump driven by a motor 105 and other components inside a housing, is installed in the brake circuit 103 that connects the master cylinder 101 to each wheel brake 102.
Moreover, a pressure control valve 106 can be installed within the rear wheel system of brake circuit 103. Such a valve serves to prevent the front brakes from locking before the rear brakes if the brakes are applied and the ABS does not function, thereby maintaining stability of the vehicle.
A conventional ABS system as described is subject to several difficulties. Additional space is required for the pressure control valve 106, making it more difficult to mount the device. The pressure control valve 106 must be mounted separately from the antilock brake device, thereby increasing the number of installation steps and attendant cost. Since the pressure control valve 106 is separate and independent from the antilock brake device, a separate housing to mount the internal parts of the pressure control valve 106 is required, which increases both the cost and the weight of the overall device. Installing the pressure control valve 106 inside the brake circuit creates a large number of pipe joints and increases the danger of brake fluid leaks. Incorporation of the pressure control valve 106 inside the antilock brake device 104 has been proposed, but in such a case, the housing must be enlarged, making the device more difficult to mount. As well, the housing must be of an unique structure requiring more tools and equipment for its construction. The attendant manufacturing costs precludes the usage of the device.